1. Field of the Invention
The present invention relates to a gas compressor suitable for automotive air conditioning or the like and adapted to suck, compress, and discharge refrigerant gas.
2. Description of the Related Art
FIGS. 10 and 11 show an example of a gas compressor for use in automotive air conditioning or the like. This compressor is equipped with a cylinder 5 with an elliptical inner periphery, and a front side block 6 and a rear side block 7 arranged at the axial ends of the cylinder 5. Inside the cylinder 5, a rotor 11 is arranged so as to be rotatable around a rotor shaft 10. A plurality of vane grooves 12 are formed so as to extend from the outer peripheral surface to the inner periphery of the rotor 11, and vanes 15 are respectively accommodated in the vane grooves 12 so as to be capable of projecting from and retracting into the vane grooves. Formed at the bottom portion (inner peripheral side) of each vane groove 12 is a back pressure chamber 14 to which pressure fluid is supplied. The vanes 15 are caused to project toward the outer periphery by the pressure of the pressure fluid supplied to the back pressure chambers 14 and the centrifugal force generated by the rotation of the rotor 11, slidably abutting the inner peripheral surface of the cylinder. In this way, the outer peripheral surface of the rotor 11, the vanes 15 projecting from the outer peripheral surface of the rotor 11 to abut the inner surface of the cylinder, and the inner peripheral surface of the cylinder 5 define a plurality of cylinder compression chambers 16. This is how the compressor main body is constructed.
In the above gas compressor, when the rotor 11 is rotated around the rotor shaft 10, the volume of the cylinder compression chambers 16 is varied, thereby compressing refrigerant gas in the cylinder compression chambers 16. The compressed refrigerant is discharged from the cylinder compression chambers 16 into an oil separating block 25. In the course of its suction, compression, and discharge, the refrigerant gas gets mixed with oil inside the gas compressor, and is discharged into the oil separating block 25 while containing the oil, which is separated from the refrigerant gas by an oil separator 26 provided in the oil separating block 25. The separated oil is dripped into an oil sump 30 to stay therein, and the compressed gas from which the oil has been removed is discharged into a second discharge chamber 8. Due to the difference in pressure inside the compressor, some of the oil in the oil sump 30 is sent under pressure through an oil passage 31, etc. to the sliding portions of the cylinder compression chambers 16 to prevent wear and effect sealing by means of oil film. Further, part of the oil is supplied to the back pressure chambers 14 as pressure fluid.
In supplying oil to the back pressure chambers 14, the vane back pressure is controlled in the course of suction, compression, and discharge strokes such that the vane back pressure is at middle pressure from the suction to compression stroke and high pressure in the discharge stroke. The reason for this is as follows. During the period in which the compression of the refrigerant gas trapped in the cylinder compression chambers 16 by means of the vanes 15 is so progressed as to attain the discharging stage, that is, in the discharge process, a strong force due to the increase in the pressure of the refrigerant gas in the cylinder compression chambers 16 is exerted so as to push the vanes 15 back toward the interior of the vane grooves 12. Thus, it is necessary to apply high pressure to the back pressure chambers 14 to press the vanes 15 reliably against the inner surface of the cylinder 5. On the other hand, during the period in which there is no need to impart a pushing out or an extruding force to the vanes 15 by means of high back pressure, that is, from the suction to the compression process, imparting large pressure to the vanes 15 only results in an increase in the rotation load of the rotor 11, which is of no use. During this period, the pressure imparted to the vanes 15 is reduced to reduce the rotation load of the rotor 11.
Thus, as shown in FIG. 11, there are provided in the end surface of the rear side block 7 flat groove portions 17 corresponding in position and configuration to the back pressure chambers 14 of the vanes 15 in transition from the suction stroke to the compression stroke, and oil is supplied to the flat groove portions 17 after being throttled by a bearing, etc. and reduced to a middle pressure. By supplying oil at middle pressure to the back pressure chambers 14 through the flat groove portions 17, the back pressure chambers 14 are maintained at the middle pressure, thus preventing a pressure more than necessary from being applied to the vanes 15, whereby it is possible to reduce the power burden, and, in the case of a compressor mounted in a vehicle, it is possible to achieve an improvement in terms of fuel efficiency.
Further, in the end surface of the rear side block 7, there are formed high pressure oil supplying holes 18 corresponding in position and configuration to the back pressure chambers 14 of the vanes 15 in the discharge stroke, and high pressure oil which has not been throttled is supplied to the high pressure oil supplying holes 18 through the oil passage 31. Thus, high pressure oil is supplied from the high pressure oil supplying holes 18 to the back pressure chambers 14. Due to the supply of the high pressure oil to the back pressure chambers 14 through the high pressure oil supplying holes 18, high pressure is maintained in the back pressure chambers 14, and high pressure is imparted to the vanes 15, thereby reliably bringing the vanes 15 into contact with the inner surface of the cylinder 5.
Incidentally, the flat groove portions 17 and the high pressure oil supplying holes 18 are situated such that communication is temporarily established therebetween through the back pressure chambers 14 as the rotor 11 rotates. Thus, even after the communication between them is canceled, the pressure of the high pressure oil remains in the flat groove portions 17, so that the pressure in the back pressure chambers 14 is kept high even in the suction and compression strokes, which means the power reducing effect cannot be achieved to a sufficient degree. To cope with this, a design has been made in which, as shown in FIG. 12, high pressure oil supplying holes 18a are arranged in a positional relationship such that no communication is established with the flat groove portions 17 through the back pressure chambers 14 so that the influence of the high pressure oil in the high pressure oil supplying holes may not be exerted on the flat groove portions 17. Due to this improvement, there is no fear of the high pressure oil supplied from the high pressure oil supplying holes 18a flowing directly into the flat groove portions 17, whereby the pressure in the back pressure chambers 14 is reduced to a sufficient degree in the suction and compression strokes, making it possible to reliably obtain the power consumption reduction effect during normal operation.
The above-described construction designed such that no communication is established between the flat groove portions and the high pressure oil supplying holes through the vane back pressure chambers involves no excessive increase in the vane back pressure in the suction and compression strokes, so that it is a satisfactory construction from the viewpoint of power reduction for the gas compressor. However, the oil in the compressor attains high pressure under the pressure of the discharge gas compressed in the gas compressor, so that, at the start of the gas compressor, the pressure of the discharge gas is not raised immediately, with the oil pressure being low. The oil supplied to the back pressure chambers in the suction and compression strokes further undergoes pressure reduction through the bearing, etc. to attain a still lower pressure. When, as is the case such as immediately after its mounting, the gas compressor is started with the vanes staying inside the vane grooves, it is necessary to push out the vanes by using the vane back pressure before the vane can be projected from the vane grooves overcoming the resistance of the oil film. However, in the above-described conventional construction, in which the vane back pressure is kept at a low level, the extruding or pushing out force during the period in which the oil pressure has not been increased to a sufficient degree yet, is insufficient, so that it may take time for the vanes to be projected. And, during the period in which the vanes have not been projected yet, normal compressing operation is not conducted, so that as long as the above phenomenon persists, the gas compressor cannot function as such. Further, there is the problem of noise (chattering) due to the collision of the vanes, slightly protruding from the outer periphery of the rotor, with the cylinder before the projection of the vanes.
Further, depending on the running condition of the vehicle, etc., when the gas compressor is operated continuously such that the rotor rotates at low speed, it is impossible to impart sufficient pressure to the vane back pressure chambers due to the low speed rotation. Further, in this state, the pressure of the refrigerant gas applied to the forward ends of the vanes overcomes the vane extruding force to push back the vanes (or the chattering limit is exceeded), and the vanes hit the cylinder inner surface as the rotor rotates, thereby generating colliding sound. It might be possible to cope with this problem by adjusting the vane back pressure in accordance with the chattering limit (increasing the pressure when imparting low pressure). However, increasing the pressure at the time of imparting low pressure would result in a deterioration in the above-mentioned power reducing effect.